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Turbomachinery Solutions for Green and Renewable Energy

Wednesday, 01 May 2013

Page 2 of 3

Hydroelectric Turbines

In many regions, the damming of
rivers and streams to manage flows for
hydroelectric generation has been an
environmental disaster. As a result, it is
highly unlikely that new hydro-electric
dams will be permitted in the U.S., with
the exclusion of dams for flood control,
irrigation, and navigation.

There is still potential for improving
the “water to wire” efficiency of most
existing hydropower turbines, and with
no further negative consequence to the
environment. And there is also enormous
potential for new hydroelectric
designs that can provide continuous and
predictable power from various lowhead,
low-power water flows — without
the need for dams — that may also vary
dramatically by location or season. With
an energy density 850 times greater than
wind, even slowly flowing waters can be
an effective energy resource for a highly
efficient hydrokinetic turbine.

Current and planned hydrokinetic
technologies are attempting to extract
the maximum amount of energy from
stream and river flows (as low as four to
five knots) without the need for dams.
The higher efficiencies progressively
achieved by these systems will ultimately
determine the extent of their feasible
applications. These same turbo-green
technologies are also planned to operate
effectively in the low flows of underground
streams and falling water. The
underwater streams of ocean estuaries
are an especially reliable energy resource
for driving a hydrokinetic turbine.

Tidal-Current and
Wave-Compressor Turbines

Within the mix of natural (and
national) energy resources, the enormous
potential in repetitive ocean waves
and tidal currents is now being
addressed by several turbo-green technologies
that propose to most efficiently
extract energy without affecting the flow
or the environment. Because all waterflow
and wave-powered systems operate
in a relatively harsh environment, turbomachinery
must be designed to operate
at peak effectiveness over a wide range
of conditions, as well as be optimized for
reliability and durability.

One promising technology is a tidalcurrent
turbine designed to harness
energy from various marine currents.
The unique Golay vertical-axis tidal-current
turbine uses hydrofoil blades
placed helically around an axis to operate
bidirectionally as tides go in and out.
An underwater tidal turbine farm would
operate much like an offshore wind
farm except for the added complexities
involved in a relatively harsher underwater
environment.

Another turbo-green solution uses an
oscillating water column (OWC) to capture
and convert ocean-wave energy into
compressed air to drive an air-turbine
generator. Ascending and descending
waves alternately compress and evacuate
air inside a chamber to drive the air-turbine-
powered generator. The core technology
incorporates a patented high-efficiency,
variable-pitch turbine in
which an electromechanical blade-pitch control enables rotation in the same
direction irrespective of the bidirectional
airflow of the OWC system.

Geothermal Pumps and Turbines

Newer geothermal electric-power
plants using binary-cycle systems are
capable of operating efficiently at relatively
low temperatures of about 225 to
360 °F (compared to dry-steam or flashsteam
plants). However, to further
reduce the high capital cost per kilowatt
of power generated, there is a great
incentive to modify the turbomachinery
used in this Organic Rankin Cycle
(ORC) in an attempt to achieve maximum
potential effectiveness that would
reduce the high capital cost per kilowatt
of power generated.

In a typical geothermal ORC cycle, a
pump transfers hot geothermal brine
from the production well to a vaporizer
where the fluid’s heat is transferred to an
organic refrigerant. The cooled brine is
then pumped into a reinjection well. In a
second loop, a pump circulates the vaporized
refrigerant to power a turbine generator.
The refrigerant is then condensed
and pumped back to the preheater to
again be vaporized in the unfired boiler
heated by the hot geothermal fluid.

To obtain meaningful improvements,
these turbomachinery systems require
more efficient pumps and turbines. One
such gravity head energy system (GHES)
uses a compact and highly efficient
turbo-expander pump installed deep
within the wellbore. This highly advanced turbo-green design significantly
increases the overall cycle efficiency by
at least 20% and up to 30%.

Biomass Steam Turbines

A wood-chip-fired boiler can generate
pressurized steam at 950 °F to drive a steam turbine, and biomass power plants
can operate 24/7 or on call as needed.
And although steam-turbine technology
in a biomass cycle is considered quite
mature, advanced capabilities in turbomachinery
design will now allow even
higher efficiencies, cleaner emissions,
and reduced expenses.

Steam turbines have long been a natural
green energy choice for onsite CHP
plants with access to a nearby supply of
low-cost biomass fuel. On a utility scale,
a biomass-fueled steam-turbine plant is
limited only by the size of the renewable
“wood basket” available within a 30- or
40-mile radius. In heavily wooded
regions, several operators of coal-fueled
power plants are now converting to burn
much cleaner biomass wood chips —
and this trend is increasing.

The low-grade wood typically harvested
for biomass fuels is mostly scrap from
forestry management over a 40-year
growth cycle. However, biomass resources are expected to dramatically
increase as second-generation biomass
fuels are produced from annual corn
and switchgrass harvests. And a new type
of tree with high fuel value and a 3-year
growth cycle is now being genetically
engineered specifically for biomass.

Biogas Turbines

Methane gas and other biogas wastes
that are environmentally harmful
byproducts of aging landfills, municipal
wastewater treatment processing, and
farm digesters can economically fuel
clean-burning gas turbines that provide
continuous electricity at efficiencies and
rates approaching or comparable to a
utility. Combined efficiencies are especially
favorable (approaching 90%)
when both the electricity and the heat
produced by the turbine can be utilized
in a CHP application.

Today’s second- and third-generation
microturbines are now employing
advanced and refined turbomachinery
designs that permit operation at higher
temperatures to achieve ever better efficiencies
and cleaner emissions. And
new turbine designs are in development
for multifuel hybrid cycles that might, as
in one case, operate alternatively on biogas
fuel when solar-thermal energy is
not available.

Many sites currently operating reciprocating-
engine generators on biogas
are retrofitting microturbines for onsite
power because the latest turbomachinery
technology provides significantly
lower emissions, better reliability, longer service intervals, and reduced maintenance.
Microturbine development is
now focused on design advancements
and technology breakthroughs that
could eventually nearly double current
efficiencies.

Question of the Week

This week's Question: This month, the Federal Aviation Administration proposed long-awaited rules on the commercial use of small drones, requiring operators to be certified, fly only during daylight, and keep their aircraft in sight. The ruling,...